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# Black Iron BTU Capacity

Member Posts: 7
Hello everyone,

I am running into an issue where I need to know the BTU capacity of 1-1/4" SCH40 Black Iron pipe. The pipe is in a hot water heating system. I've been looking for charts online and I can't find what I am looking for. Does anyone here know of any charts, or can provide information for what I am looking for.

Thank you

## Comments

• Member Posts: 1,296
How many btu are we talking about…?
• Member Posts: 1,296
120 for 1-1/4.
200 for 1-1/2
I think it’s a little more but that’s what I just found
• Member Posts: 7
Are you able to share your source with me?
• Member Posts: 1,296
Just google black pipe water btu….. nothing special
• Member Posts: 804
google this

heat loss of 1 1/4" schedule 40 black steel pipe

Jake
• Member Posts: 11,188
If you looking for water flow btu capacity 1 1/4" will carry 16 gpm max. If your system has a 20 degree temperature drop you are good for 160,000 btu/hour (10,000 btu/gpm circulated)
• Member Posts: 7
Thank you all for your help. I was over thinking my Google search.
• Member Posts: 3,046
This calculator will give you GPM as a function of feet per second.

https://www.tlv.com/global/US/calculator/water-flow-rate-through-piping.html
Often wrong, never in doubt.
• Member Posts: 7,139
BTU/Hr = GPM x Delta T x 500 (constant)
Many designers use GPM at 4 ft/sec and a Delta T of 20 degrees.
For "speed math" you can take the pipe capacity at 4 ft/sec and just move the decimal.
16 GPM x 20 X 500 +160,000
"If you can't explain it simply, you don't understand it well enough"
Albert Einstein
• Member Posts: 15,428
The engineering toolbox has a lot of info for sizing pipes, here is a type L copper example and steel pipe 2" and up.

Pipe size over 2" is sized by pressure drop, not the flow velocity. Pipe under 2" stay at or below 4 fps velocity.

So the table shows max. flow rates, now determine the delta T you will design around to get heat carrying capacity.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream